The present invention relates to a developing device for use in an electrophotographic apparatus which is applicable for use with printers, facsimile apparatuses, copying machines, and the like.
The configuration of a known developing device is shown in FIG. 6. Referring to FIG. 6, reference numeral 1 denotes a developing roll for forming a thin layer of electrically charged tonor thereon and transporting the tonor to a photosensitive member; 2 denotes a transport roll for transporting the tonor to the developing roll 1; 3 denotes a tonor transporting vane for agitating the tonor and transporting the tonor to the transport roll; 5 denotes a regulating blade for regulating the amount of the tonor attaching onto the developing roll 1; 6 denotes a tonor storage for storing tonor; 9 denotes tonor; and 10 denotes a photosensitive member 10.
In a conventional developing device of the one-component type, the photosensitive member 10 is generally disposed so that at the tonor transfer position, it moves downward, and the developing roll 1, with a tonor thin layer formed thereon, is also arranged to rotate downward at the tonor transfer position facing the photosensitive member 10 to perform development.
The tonor 9 within the tonor storage 6 is transported to the transport roll 2 by the rotating tonor transporting vane 3. As the transport roll 2, a conductive or semiconductive foam roll is generally used. The tonor 9 transported to the transport roll 2 is further transported to the developing roll 1 by the rotating transport roll 2. The amount of tonor is regulated by the regulating blade 5 provided on the developing roll 1 and the tonor is electrically charged by friction with the regulating blade 5 to form a thin layer of charged tonor on the developing roll 1. The developing roll 1 with the charged tonor thin layer formed thereon, when brought into contact with or into the vicinity of the photosensitive member 10, develops an electrostatic latent image on the photosensitive member 10.
In the configuration of the developing device of FIG. 6, because the developing roll 1 is located below the regulating blade 5, tonor can be supplied in a stabilized manner to the regulating position of the regulating blade 5 located on the surface of the developing roll 1. Further, since the tonor which has become a surplus by the action of the regulating blade 5 can escape into the space above the regulating blade, a flow of tonor shown by an arrow 28 in the drawing is produced, and, thereby, the surplus tonor is returned, in a stabilized manner, to the transport roll 2 and the tonor storage 6 so as to be circulated. Thus, a stabilized tonor supply to the regulating blade 5 and the recovery of the surplus tonor can both be achieved, so that the tonor is prevented from stagnating or solidifying.
On the other hand, in the case of a developing device of a nonmagnetic one-component type in which the photosensitive member 10 is positioned to move upward at the tonor transfer position, it is necessary to cause the developing roll 1 with a tonor thin layer formed thereon also to rotate upward to perform development at the tonor transfer position facing the photosensitive member 10. Since, in this case, it is necessary to dispose the regulating blade 5 below the developing roll 1, it becomes difficult to supply the tonor to the regulating position of the regulating blade 5 on the surface of the developing roll 1 in a stabilized manner. Further, since the surplus tonor provided by the regulating blade 5 falls below the developing roll 1 due to gravity, it becomes difficult to form a circulating path as shown by the arrow 28 in FIG. 6 within the developing device.
A developing device for performing development using a developing roll 1 with a tonor thin layer formed thereon, which is rotated upward at the tonor transfer position facing the photosensitive member 10, is disclosed in the Japanese Patent Laid-open No. Hei 5-158345. The configuration of this developing device is shown in FIG. 7. Reference numerals used in FIG. 7 correspond to those in FIG. 6.
Referring to FIG. 7, there are formed a passage 29 for transporting tonor to the side of the developing roll 1 and a passage 30 for transporting the remaining tonor after the regulation by the blade has been made back to the tonor storage 6 so that the tonor 9 may be circulated. Further, there is disposed a transport roll 2 for assisting in the tonor supply to the regulating blade 5.
In addition to the above developing device, there is disclosed in the Japanese Patent Laid-open No. Hei 5-158331 a developing device in which the developing roll 1 performs development while rotating upward at the tonor transfer position facing the photosensitive member 10 and the regulating blade 5 is located above the developing roll 1. By such a configuration, it is intended to decrease the chances for the tonor to be repeatedly subjected to regulation by the regulating blade and to supply tonor of good quality for development to obtain a high quality image.
However, in the developing device disclosed in Japanese Patent Laid-open Publication No. Hei 5-158345, since the opening of the supply passage on the side of the developing roll is connected with the opening on the side of the return, recovery passage, namely, since the space on the side of the supply passage and the space on the side of the recovery passage are not completely separated from each other, it is difficult to simultaneously achieve a stabilized supply of the tonor to the vicinity of the regulating blade and a recovery of the surplus tonor regulated by the regulating blade. Therefore, in order to supply the tonor to the regulating blade 5 in a stabilized manner in the developing device disclosed in Japanese Patent Laid-open No. Hei 5-158345, it is required to maintain a stabilized tonor layer in contact with the surface of the transport roll under a certain amount of force and a space for allowing the tonor subjected to the regulation to flow out through it in a stabilized manner.
On the other hand, with the developing device disclosed in Japanese Patent Laid-open No. Hei 5-158331, since the passage for supplying the tonor to the regulating blade and that for recovering the tonor are required to be arranged above the developing roll, there is a disadvantage in that the overall developing device becomes greater in thickness and, therefore, larger in overall size.
In the developing device disclosed in the Japanese Patent Laid-Open No. Hei 5-158331, in which development is performed by rotating the developing roll with a tonor thin layer formed thereon upward at the tonor transfer position facing the photosensitive member to develop the surface of the photosensitive member, while it is moving upward, it is required that the regulating blade be disposed at the side of or below the developing roll. However, when the regulating blade is disposed below the developing roll, it becomes difficult to supply the tonor to the regulating position of the regulating blade on the surface of the developing roll in a stabilized manner.
In order to stably supply the tonor to the vicinity of the regulating blade, it is required to fill up the area in the vicinity of the regulating blade with tonor. However, in a state in which the area in the vicinity of the regulating blade is filled up with tonor, it becomes difficult to allow the surplus tonor subjected to the regulation by the regulating blade to escape and, hence, the tonor tends to produce cake of tonor. When, conversely, it is arranged to make it easier for the tonor subjected to the regulation by the regulating blade to escape, then, since the regulating blade is located below the developing roll, it becomes difficult to stably supply the tonor to the area in the vicinity of the regulating blade and, hence, it becomes difficult for the regulating blade to form a stabilized tonor thin layer.
For these reasons, it is the present state of the art that the one-component developing type, in spite of its being smaller and simpler in structure than the two-component developing device, is only applied to a limited range of photographic printer configurations in which the photosensitive member rotates downward at the tonor transfer point. If a one-component developing device capable of achieving stabilized development also when applied to photographic print systems having a photosensitive member rotating upward at the tonor transfer point can be realized, restrictions on the overall configuration of the device will be reduced and, hence, it will become possible to provide a smaller and more stabilized electrophotographic apparatus.